Engine exhaust line is damage

Engine exhaust line is damage

Engine exhaust line is damage

i am working in a gas compression plant,recently we are facing the engine back fire issue in startup
because of that exhaust lines damaged twice.
The engine we have here is CAT-3616 series,(Almost run-42,000 ) coupled with Ariel-JGC6
engine RPM is maximum 1000,but we reduced to 960 due to vibration issue.

i will give a brief how this is happening.
when you give a start command to the engine,ECM will initiate starting sequence,starting motor will engage & completed its cycle,(Purge,ignition,)then disengage.
during this time engine back fired twice,even though it was in startup sequence.

one of our service tech given advice,that you should keep open compressor PID controlled recycle valve bypass as well to reduced the engine load in startup.
i bit of confused that,how come the bypass opening will help,because recycle valve is already opened until unit will come on line.
any suggestion?

RE: Engine exhaust line is damage

internal combustion engine backfire is a result of fuel burning/igniting in exhaust system. this could be a result of exhaust valve timing (opening too early), somehow the fuel/air mixture in exhaust is ignited by?.
i recommend checking the engine fuel and exhaust system, possibly engine timing too.
also, the engine should be started in an "unloaded" state - meaning the compressor is in bypass mode. once the engine is started and achieved ready to compress gas state, close the bypass slowly. note that recycling gas (open bypass) may result in excessive gas temperatures, which should be monitored.
good luck!

RE: Engine exhaust line is damage

Given you're new, it is always good if you can attach a sketch or drawing so we can understand what you mean as "recycle" and "bypass" can mean the same thing and it is difficult to understand what you mean - "PID controlled recycle valve bypass " is meaningless without a drawing.

Remember we only know or can see what you tell us, so re-read the post before you post it and think what might someone else need to understand my problem that I've not written down or shown on my sketch / drawing/ If you don't want to send original drawings, then do a hand sketch of the key items and scan it.

Basically reduce load to minimum on start, but also check engine fuel system and timing as noted above.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Engine exhaust line is damage

On a typical recip compressor, driven by a natural gas engine, there's both a an auto-recycle control valve, as well as a startup bypass. The auto-recycle will be sized for capacity control, but usually this sizing leads to a recycle valve which isn't appropriate for startup. That's where the startup bypass comes in. It's usually a manual ball valve, sized to put no load on the compressor when in bypass mode.

So I'm guessing that you have the recycle valve 100% open, but not the bypass valve. The recycle valve is probably putting excess load on the engine, as the compressor has to push a bit harder to squeeze the gas through the port in the recycle valve. If you open the bypass valve, the loading on the compressor is minimized.

I would suggest trying a startup with both the recycle valve and the bypass valve open. If this fixes your issue, great. Otherwise, it's probably something to do with the engine timing and configuration, but I can't provide any advice on that front other than to consult a Caterpillar mechanic.

RE: Engine exhaust line is damage

Would be helpful to have some additional details about the engine and package, there are currently 3 major controls types for G3600 engines in compression service, all are electronic controls and require using the CAT PC based service tool (CAT ET).

If you are at 42,000 hours, have you done any recent major work, like a major service or overhaul? You also mentioned an "excessive vibration" causing you to reduce unit output, did your starting problem appear about the same time as the vibration?

You may have some better luck at the CAT Forums, http://forums.cat.com/, as they have a specific area just for gas compression and some really experienced gas engines guys are active on that site. If you go there please post your serial number and who packaged the compressor, helps get you the best possible answers.

MikeL.

RE: Engine exhaust line is damage

in reading catserveng posting, i recalled a similar electrical matter, but this case generated detonation problems. the electrical cabling on the engine was encased inside a metal conduit. when the engine/compressor was operating, the cabling vibrated inside the conduit causing mild short-circuits and other strange engine malfunctions. eventually, the cabling + conduit was replaced; thereby, correcting the problem. so, yes, perhaps there may be loose electrical connections or a cable has some insulation loss, which may generate control system malfunctions. i'm not sure how to check cable insulation when installed inside a conduit. i'm sure the sparkys know of a method.

good luck!

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